In recently years, the surface acoustic wave (SAW) sensors employing magnetostrictive thin film as sensitive interface has provided a new approach to exploit magnetic field sensing. A group led by researcher WANG Wen from the Institute of Acoustics of the Chinese Academy of Sciences (IACAS) once proposed a FeCo thin-film coated SAW device for sensing current/magnetic field, obtained sensitivity was up to 8.3KHz/mT based on the theoretical optimization.

JIA Yana, a doctoral student from IACAS, along with her mentor WANG Wen and three other researchers, designed a new grating-patterned magnetostrictive FeCo coated surface acoustic wave (SAW) device for sensing magnetic field, with high sensitivity and low hysteresis.

The new grating-patterned magnetostrictive FeCo coated SAW sensor is composed of a configuration of differential dual-delay-line oscillators, and a magnetostrictive FeCo grating array deposited along the SAW propagation path of the sensing device, which effectively suppresses the hysteresis effect by releasing the internal binding force in FeCo. Figure 1 describes the schematic views of the sensor.

Figure 1. The scheme of the proposed SAW magnetic field sensor. (Image by IACAS)

The magnetostrictive strain and ΔE effect from the FeCo coating modulates the SAW propagation characteristic, and the corresponding shift in differential oscillation frequency evaluates the measurant.

Experimental results, as shown in Figure 2, indicate that the new grating-patterned FeCo coated sensor has higher sensitivity, excellent linearity, and lower hysteresis error over the typical FeCo thin-film coated sensor, with the hysteresis effect in FeCo suppressed.

Figure 2. The continuous response and sensitivity evaluation of the proposed sensor with FeCo grating array, in comparison with FeCo thin-film coated sensor. (Image by IACAS)